Add popup annotation support

[MartinThoma]

Explanation

More complete feature support for annotations.

Code Example

Just like the other annotations

Hints

• TABLE 8.34 Additional entries specific to a pop-up annotation
• See Tutorials or better demos to manipulate annotations #107

[MartinThoma]

A document with a popup is https://corpora.tika.apache.org/base/docs/govdocs1/919/919218.pdf. In my PDF viewer, it looks like this:

from PyPDF2 import PdfReader

reader = PdfReader('pdf/0358334a06fb777fd0187836840c9e9c.pdf')
reader.pages[0].annotations[1].get_object()

gives

{
    "/Type": "/Annot",
    "/Subtype": "/Popup",
    "/Rect": [
        154.16571,
        699.16745,
        619.16168,
        786.16669
    ],
    "/Open": true,
    "/F": 25,
    "/Parent": "IndirectObject(473, 0, 139986144693936)"
}

with the reader.pages[0].annotations[1].get_object()["/Parent"]

being

{
    "/Type": "/Annot",
    "/Subtype": "/Text",
    "/Rect": [
        154,
        764,
        172,
        786
    ],
    "/Open": true,
    "/Contents": "This report is one in a series.  More recent editions may be available.  To view a list of all in the series go to http://www.ojp.usdoj.gov/bjs/pubalp2.htm#ncvs",
    "/M": "D:20010522125319-05'00\"",
    "/T": "BJS",
    "/Popup": "IndirectObject(612, 0, 139986144693936)",
    "/F": 28,
    "/AP": "IndirectObject(615, 0, 139986144693936)"
}